Hiding submit button if multiple choice question not ticked

I’m sure this is straightforward but it’s been a while since I used Qualtrics and I can’t quite nail this. I want to hide the next button on a page unless a multiple choice question is selected. It only has one choice and so in effect acts as a checkbox. I found the following code which shows the next button if ticked but cannot get it to hide it again if the question is unticked. Any advice welcome, thanks.

Qualtrics.SurveyEngine.addOnload(function()
{
	this.hideNextButton();
	this.questionclick = function(event, element) {
        if (element.type == 'checkbox') {
			var choiceNum = element.id.split('~')[2];
            if (choiceNum==1) {this.showNextButton();}
			else {this.hideNextButton()}}}
});